About liquid crystal display devices, a backlight type, in which a liquid crystal layer is irradiated from the rear surface side thereof so as to make the liquid crystal layer luminous, has been spreading. At the lower surface side of the liquid crystal layer, a backlight unit is arranged. This backlight unit is classified into an edge light type and a direct type. Even when any one of these types is adopted, the brightness distribution of light rays emitted therefrom is varied between a case where the distribution is viewed along a direction perpendicular to its linear lamp and a case where the distribution is viewed along a direction parallel thereto. In general, the brightness distribution along the direction perpendicular to the lamp exhibits a stronger peak while the brightness distribution in the direction parallel to the lamp is relatively bilaterally-symmetric and even, and less exhibits a peak in a specific direction.
On the other hand, about light-diffusing films of a bead-painted type or embossed type, the diffusivity thereof is even over all directions so as to have isotropy. Thus, it is not possible to make a control so as to remove a difference between the brightness distribution of light rays emitted as described above along the front and back direction and that along the right and left direction.
In order to correct imbalance between the brightness distributions, it has been desired to develop an anisotropic light-diffusing film different between the light diffusivity in the front and back direction and that in the right and left direction, and various techniques have been disclosed.
In many of the disclosed techniques, importance is attached to diffusivity (or scattering property; hereinafter, in the invention, diffusivity or scattering property will be consistently referred to as diffusivity). Anisotropic light-diffusing films are restricted to films covering a high haze region, or a low parallel light ray transmittance region.
For example, Patent Literature 1 or the like is known as a disclosed technique wherein the haze is restricted into a high-haze region of 85% or more in the claims thereof or the examples thereof.
Patent Literature 2 or the like is known as a disclosed technique wherein the parallel light ray transmittance is restricted into a low region in the claims thereof or the examples thereof.
By contrast, Patent Literature 3 is known as a disclosed technique wherein the haze is restricted into a low-haze region of 15% or less in the examples thereof.
Patent Literatures 4 and 5 are each disclosed as a technique wherein the haze is restricted into a middle-haze region in the examples thereof.
However, in the technique disclosed in Patent Literature 4, the film thereof is formed from a solution; thus, the technique is disadvantage from the viewpoint of economical efficiency and load onto the environment.
In the technique disclosed in Patent Literature 5, spherical silica particles are used as dispersed phases. Thus, in the process for forming the film, the clogging of a polymer filter is increased. As a result, the technique has a problem that a fine filter is not easily used and the resultant optically anisotropic film is low in clearness.
In a technique disclosed in Patent Literature 6, optical anisotropy is given by embossing. Thus, the technique is disadvantageous for economical efficiency in the same way as the above-mentioned techniques.
Patent Literature 7 is disclosed as a technique wherein the glossiness is restricted into a middle-glossiness region in the examples thereof. However, in the technique disclosed in Patent Literature 7, an acrylic resin, which is an amorphous resin, is used as a continuous phase resin. The resultant optically anisotropic film has a problem that the film is poor in solvent-resistance. Furthermore, silicone crosslinked beads are used as dispersed phases. Thus, in the process for forming the film, the clogging of a polymer filter is increased. As a result, the technique has a problem that a fine filter is not easily used and the resultant optically anisotropic film is low in clearness.
Moreover, disclosed are many techniques in each of which general optical properties, such as the haze or the parallel light ray transmittance, are not clearly described (e.g. Patent Literatures 8 to 11).
These disclosed techniques are based on a technique similar to the above-mentioned patents, wherein importance is attached to diffusivity. In many of the techniques, it is presumed that an optically anisotropic film covering a high haze region is obtained.
Furthermore, for example, in a technique disclosed in Patent Literature 8, the film thereof is produced from a solution. Thus, the technique is disadvantageous from the viewpoint of economical efficiency and load onto the environment.
In a technique disclosed in Patent Literature 9, porous acrylic particles are used as dispersed phases. Thus, in the process for forming the film, the clogging of a polymer filter is increased. As a result, the technique has a problem that a fine filter is not easily used and the resultant optically anisotropic film is low in clearness.
In a technique disclosed in Patent Literature 10, an amorphous resin is used as a resin which forms a continuous phase, examples of the resin including an ultra low density polyethylene resin, an amorphous co-polymeric polyester resin and a polystyrene resin. The technique has a problem that the resultant optically anisotropic film is poor in solvent-resistance.
In a technique disclosed in Patent Literature 11, a compatibility accelerator containing an epoxy group, which is high in reactivity, is used. Thus, the technique has a problem that in a film-forming process, crosslinking reaction is caused so that the clearness of the resultant optically anisotropic film declines.
In lighting inside a room or the like, lighting in an internal-lighting type illumination panel, light radiation in a copying machine, lighting in a liquid crystal display device, or the like, a light-reflecting sheet or light-reflecting plate, which may be referred to merely as a light reflector hereinafter, is used to make effective use of the quantity of light from a light source and heighten the illuminance or brightness of the lighting.
As the light reflector, for example, a diffusive reflecting member made of a white PET film is frequently used. The diffusive reflecting member has a property wherein importance is attached to diffusivity, and the member is low in positive reflectivity. Thus, the member gives reflectivity high in evenness; however, the member has a problem that the reflectivity is low.
On the other hand, as a method for solving the problem, a reflector has been developed wherein the luster of a metal such as aluminum or silver is used to give a high positive reflectivity. Although the method makes the reflectivity high, the directivity of the reflection is high. Thus, in indoor lighting or office lighting, a strong reflection is caused in a specific direction. Therefore, the method has problems that the reflection is short of uniformity over directions and further an intense glaringness is caused in the specific direction. The method also has a problem that the uniformity of the brightness deteriorates in lighting in an internal-lighting type illumination panel, or lighting in a liquid crystal display device. Furthermore, the method has a problem that when the reflector is partially wrinkled or warped, the uniformity of the reflection further deteriorates since the directivity of the reflection is intense.
As a method for solving the problems, suggested is a method of laminating a diffusion layer for controlling the diffusivity of light onto a surface of a light reflector using metallic luster, thereby controlling the diffusivity of reflection thereon.
However, the suggested technique is restricted to two extreme regions, which are regions wherein the light transmittance of the diffusion layer is high and wherein the transmittance is in reverse low.
As a method restricted to the high-light-transmittance region, for example, Patent Literature 12 is known.
According to the method disclosed in the Patent Literature 12, the diffusivity is improved more than any light reflector merely using metallic luster. However, the method still gives an intense directivity, and does not solve the problems which are possessed by the reflecting sheet using metallic luster.
On the other hand, as a method restricted to the low-light-transmittance region, for example, Patent Literature 13 is known.
According to the method disclosed in the Patent Literature 13, the diffusivity is largely improved. However, the positive reflectivity thereof is largely lowered. Thus, the method has the same problem as that of the light reflector made of a white reflecting film.
On the other hand, as a method for giving anisotropy of light reflection, which may be referred to merely as anisotropy hereinafter, to a light-reflecting laminate composed of a light reflector containing a metallic layer and a light-diffractive layer, disclosed is a method of subjecting a metallic layer surface to hair line processing (see Patent Literature 14).
The method may not give sufficient anisotropy. Moreover, the method has a problem that a homogeneous product is not easily obtained since an even processing is not easily attained.
As another method for giving anisotropy, disclosed is a method of combining a lens sheet or prism sheet with a light reflector containing a metallic layer (e.g. see Patent Literature 15).
The method disclosed in the patent literature is disadvantageous for economical efficiency since the lens sheet or prism sheet is expensive.
Patent Literature 15 refers to a method wherein a light reflector containing a metallic layer is combined in the text thereof. However, an example of the method is never demonstrated in examples. According to the method of the Patent Literature 15, a light-diffusing layer is made of a white reflecting film. It is presumed that even when the light-diffusing layer is combined with the light reflector containing a metallic layer, an improvement in the reflectivity is small.
Disclosed is also a method of giving anisotropy to a white reflecting film by hair line processing (see Patent Literature 16).
The method disclosed in the patent literature has a problem that a light reflector is the white reflecting film so that an excellent diffusivity is generated while the reflectivity is low.
In recent years, because of problems of global warming and the exhaustion of resources, the request of energy saving has been becoming intense also in the above-mentioned lighting field.
For example, a liquid crystal display device is used in the display section of a clock, a calculator, a TV, a personal computer, or the like at present while making good use of advantageous characteristics thereof, for example, characteristics that the display is thin, small and low in consumption power. Furthermore, in recent years, color LCDs have been developed, and the use thereof has been starting for many articles such as a car navigation system, a view finder and a monitor of a personal computer, these articles being mainly OA and AV machines. It is expected that markets therefor will rapidly expand hereafter. In particular, about reflective liquid crystal display devices, wherein incident light from the outside is reflected to attain display, no backlight is required so that consumption power is small and further the displays can be made thin and light. Thus, attention has been paid to the displays for the purpose of being used as portable terminals.
In the case of the reflective liquid crystal display devices, it is known that in the case of using the displays as portable terminals, it is preferred that high is the reflectivity thereof to light rays each having an incidence angle within ±20 degrees to their reflecting sheet. A higher-performance anisotropic light-reflecting sheet has been desired.